The Copenhagen elephants outside their new home, designed by Foster and Partners. Photograph: Lina Ahnoff

Zoo buildings are tricky commissions for architects. Even the most celebrated zoo architects have been prey to changing fashions and evolving ideas in the care of captive animals. Not so long ago, and even today in many parts of the world, zoos have been thought as little more than cabinets of living curiosities, with animals on show as if they were four-legged clowns rather than fellow creatures we should treat respectfully.

The story of Jumbo the Elephant, once told in many children's books, is instructive. Jumbo was an enormous African elephant born in 1861 and who, through various misfortunes, made his way from Angola to London Zoo. Here he was much feted by Victorian society, although the very same people fed him unkindly on hundreds of copper coins, keys and even a policeman's whistle. How do we know this? Because poor Jumbo was killed by a freight train in St Thomas, Ontario in September 1885 while being transported by P T Barnum and his famous travelling circus. The elephant had been sold on by London Zoo at a time when animal welfare was very much in its infancy and a post-mortem discovered the bull elephant's hidden treasures. It was a wonder he had lived so long, although he was really only just middle-aged.

Today, with the opening of the new Elephant House at Copenhagen Zoo designed by Foster and Partners, we can see very clearly how attitudes towards elephants, and zoo animals in general, has changed very much for the better. Jumbo would have led a very different life here.

Whether zoos should exist at all is a question that troubles many of us. But, although it would be great if animals could all roam free, the problem lies with us. Humans just can't stop themselves from wiping out entire species, whether accidentally or wilfully, and smothering the world with buildings. Zoos give us the chance to nurture endangered species and, who know, one day we might, collectively, learn to be kind to animals and agree to share the world fairly with them.

How, though, can anyone really provide elephants with an ideal habitat in a Scandinavian city? How are penguins expected to cope with fetid London summers? And, how can curators, keepers and architects balance the need to show animals to the public who pay for tickets to see lions and giraffes, scary spiders the size of your hand and performing seals with a proper concern for their welfare?

Berthold Lubetkin, the Russian emigré architect, designed the Grade 1 listed Penguin Pool at London Zoo, opened in 1934, a building well worth seeing even when devoid of animal life. Although Lubetkin studied what was known at the time about the life of his future tenants and provided them with the best floor surfaces he could, the zoo decided to concrete over the surfaces, making these very hard on the feet of the luckless birds. Lubetkin was then criticised for getting it wrong. Equally, he was asked to design for Antarctic penguins, a very different breed from the South African penguins who replaced their southerly kin in later years. They penguins didn't take kindly to the Lubetkin design - it wasn't intimate enough for them - and so, again, the architect was in the dog house.

I tell this story just so we're all clear that designing homes for animals is a very difficult thing to do indeed. How can any architect even begin to match the subtlety of a spider's web or recreate the landscapes and forests elephants call home? Zoo architecture is, at best, an art, or beast, of uneasy and uncertain compromise. Which, though, do you think work well, and which do you think should be fed, as it were, to the lions?